Highly conserved and extremely variable: the paradoxical pattern of toxin expression revealed by comparative venom-gland transcriptomics of Phalotris (Serpentes: Dipsadidae)

Although non-front fanged snakes account for almost two-thirds of snake diversity, most studies on venom composition and evolution focus exclusively on front-fanged species, which comprise most of the clinically relevant accidents. Comprehensive reports on venom composition of non-front fanged snakes are still scarce for several groups. In this study, we address such shortage of knowledge by providing new insights about the venom composition among species of Phalotris, a poorly studied Neotropical dipsadid genus. Phalotris are known for their specialized venom delivery system and toxic venoms, which can cause life-threatening accidents in humans. We evaluate the venom-gland transcriptome of Phalotris, comparing the following three South American species: P. reticulatus for the Araucaria Pine forests, P. lemniscatus for the Pampa grasslands, and P. mertensi for the Brazilian Cerrado. Our results indicate similar venom profiles, in which they share a high expression level of Kunitz-type inhibitors (KUNZ). On the other hand, comparative analyses revealed substantial differences in the expression levels of C-type lectins (CTL) and snake venom metalloproteinases (SVMP). The diverse set of SVMP and CTL isoforms shows signals of positive selection, and we also identified truncated forms of type III SVMPs, which resemble type II and type I SVMPs of viperids. Additionally, we identified a CNP precursor hosting a proline-rich region containing a BPP motif resembling those commonly detected in viperid venoms with hypotensive activity. Altogether, our results suggest an evolutionary history favoring high expression levels of few KUNZ isoforms in Phalotris venoms, contrasting with a highly diverse set of SVMP and CTL isoforms. Such diversity can be comparable with the venom variability observed in some viperids. Our findings highlight the extreme phenotypic diversity of non-front fanged snakes and the importance to allocate greater effort to study neglected groups of Colubroidea.

Phylogenomic discordance is driven by wide-spread introgression and incomplete lineage sorting during rapid species diversification within rattlesnakes (Viperidae: Crotalus and Sistrurus)

Phylogenomics allows us to uncover the historical signal of evolutionary processes through time and estimate phylogenetic networks accounting for these signals. Insight from genome-wide data further allows us to pinpoint the contributions to phylogenetic signal from hybridization, introgression, and ancestral polymorphism across the genome. Here we focus on how these processes have contributed to phylogenetic discordance among rattlesnakes (genera Crotalus and Sistrurus), a group for which there are numerous conflicting phylogenetic hypotheses based on a diverse array of molecular datasets and analytical methods. We address the instability of the rattlesnake phylogeny using genomic data generated from transcriptomes sampled from nearly all known species. These genomic data, analyzed with coalescent and network-based approaches, reveal numerous instances of rapid speciation where individual gene trees conflict with the species tree. Moreover, the evolutionary history of rattlesnakes is dominated by incomplete speciation and frequent hybridization, both of which have likely influenced past interpretations of phylogeny. We present a new framework in which the evolutionary relationships of this group can only be understood in light of genome-wide data and network-based analytical methods. Our data suggest that network radiations, like seen within the rattlesnakes, can only be understood in a phylogenomic context, necessitating similar approaches in our attempts to understand evolutionary history in other rapidly radiating species.

Molecular phylogeny and biogeography of the dwarf boas of the family Tropidophiidae (Serpentes: Alethinophidia)

Although present in the South American continent, dwarf boas (Tropidophiidae) show their greatest extant diversification in the Caribbean region, reaching their highest diversity in Cuba. Despite their remarkable species richness, phylogenetic affinities among species of Tropidophis and Trachyboa are still poorly known. Here, we provide a multi-locus phylogenetic hypothesis of the family that includes 25 of the 37 known continental and insular species, including most of its highly diverse Cuban endemic radiation (16 out of 17 species sampled). We also provide a time-calibrated tree derived from our molecular data. Our phylogenetic results indicate that the genus Tropidophis and its mainland and Cuban radiations are paraphyletic, while the Caribbean radiation forms a well-supported clade. We therefore synonymize Trachyboa with Tropidophis and provide new definitions for the species groups. Our time-calibrated tree suggests that tropidophiids originated along the northwestern Andean region of continental South America, diverging from its known sister-group genus Anilius during the late Cretaceous. The Atlantic Rainforest radiation diverged from the Andean radiation during the late Eocene. A mainland tropidophiid ancestor subsequently dispersed from northern South America to the Caribbean region in the latest Eocene. Dispersal likely took place through a near-continuous terrestrial land bridge that connected South America to the Greater Antilles during the late Eocene to early Oligocene (35–33 Ma). The existence of this land bridge, whether formed by the Aves Ridge (GAARlandia Hypothesis) or by a more southernly positioned landmass connecting the Greater Antilles and the northern Lesser Antilles Ridge (GRANoLA hypothesis), remains a topic of debate, which we address in this paper. After that main dispersal event, West Indian tropidophiids underwent over ten speciation events, rapidly colonizing the Caribbean islands. We also address the vertebral morphology of fossil and extant Tropidophiidae, with our observations challenging the current classification of several fossil taxa within crown-Tropidophiidae.

Venom composition of neglected Bothropoid snakes from the Amazon Rainforest: ecological and toxinological implications

Snake venoms have evolved in several families of Caenophidae, and their toxins have been assumed to be biochemical weapons with a role as a trophic adaptation. However, it remains unclear how venom contributes to the success of venomous species for adaptation to different environments. Here we compared the venoms from Bothrocophias hyoprora, Bothrops taeniatus, Bothrops bilineatus smaragdinus, Bothrops brazili, and Bothrops atrox collected in the Amazon Rainforest, aiming to understand the ecological and toxinological consequences of venom composition. Transcriptomic and proteomic analyses indicated that the venoms presented the same toxin groups characteristic from bothropoids, but with distinct isoforms with variable qualitative and quantitative abundances, contributing to distinct enzymatic and toxic effects. Despite the particularities of each venom, commercial Bothrops antivenom recognized the venom components and neutralized the lethality of all species. No clear features could be observed between venoms from arboreal and terrestrial habitats, nor in the dispersion of the species throughout the Amazon habitats, supporting the notion that venom composition may not shape the ecological or toxinological characteristics of these snake species and that other factors influence their foraging or dispersal in different ecological niches.

There and back again: when and how the world's richest snake family (Dipsadidae) dispersed and speciated across the Neotropical region

Aim The widespread megadiverse Neotropical snake family Dipsadidae occurs in a large range of diverse habitats. Therefore, it represents an excellent model to study the diversification of Neotropical biota. Herein, by generating a time-calibrated species-level phylogeny, we investigate the origin and historical biogeography of Dipsadidae and test if its two main Neotropical subfamilies, Xenodontinae and Dipsadinae, have different geographical origins. Location Neotropical region. Taxon Dipsadidae (Serpentes). Methods We generated a new Bayesian time-calibrated phylogeny based on published sequences from six genes for 344 species, including 287 species of Dipsadidae. We subsequently estimated ancestral areas of distribution by comparing models in BioGeoBEARS: DEC (subset sympatry, narrow vicariance), DIVALIKE (narrow and wide vicariance), BAYAREALIKE (no vicariance and widespread sympatry), also testing jump dispersal. We also estimated shifts in the diversification of this group using BAMM, exploring possible relationships with its historical biogeography. Results The best models show that Dipsadidae likely originated approximately 50 million years ago (mya) in Asia. Dispersal was a fundamental process in its historical biogeography. The DEC model with jump dispersal indicated that this family underwent a range extension from Asia and posterior vicariance of North and Central America ancestors. Both Xenodontinae and Dipsadinae originated in Central America and dispersed to South America during Middle Eocene, but did so to different regions (cis and trans-Andean South America, respectively). Xenodontinae entered cis-Andean South America around 39 mya and jump dispersed to the West Indies around 33 mya, while Dipsadinae entered trans-Andean South America multiple times 20–38 mya. The diversification rate decreased through time, except for a clade within Dipsadinae composed of the Dipsadini tribe and the Atractus and Geophis genera. Main Conclusions Our results show that Dipsadidae has an Asian origin and that the two main Neotropical subfamilies originated in Central America, later dispersing to South America in different time periods. This difference is also reflected in the higher diversification rate for the ‘goo-eaters’ in the Dipsadinae subfamily. The current biogeographical patterns of the family Dipsadidae, the most species-rich snake family in the world, have likely been shaped by complex evolutionary and geological processes such as Eocene land bridges, Andean uplift and the formation of the Panama isthmus.

The Venom Composition of the Snake Tribe Philodryadini: 'Omic' Techniques Reveal Intergeneric Variability among South American Racers.

Snakes of the Philodryadini tribe are included in the Dipsadidae family, which is a diverse group of rear-fanged snakes widespread in different ecological conditions, including habitats and diet. However, little is known about the composition and effects of their venoms despite their relevance for understanding the evolution of these snakes or even their impact on the occasional cases of human envenoming. In this study, we integrated venom gland transcriptomics, venom proteomics and functional assays to characterize the venoms from eight species of the Philodryadini tribe, which includes the genus Philodryas, Chlorosoma and Xenoxybelis. The most abundant components identified in the venoms were snake venom metalloproteinases (SVMPs), cysteine-rich secretory proteins (CRISPs), C-type lectins (CTLs), snake endogenous matrix metalloproteinases type 9 (seMMP-9) and snake venom serinoproteinases (SVSPs). These protein families showed a variable expression profile in each genus. SVMPs were the most abundant components in Philodryas, while seMMP-9 and CRISPs were the most expressed in Chlorosoma and Xenoxybelis, respectively. Lineage-specific differences in venom composition were also observed among Philodryas species, whereas P. olfersii presented the highest amount of SVSPs and P. agassizii was the only species to express significant amounts of 3FTx. The variability observed in venom composition was confirmed by the venom functional assays. Philodryas species presented the highest SVMP activity, whereas Chlorosoma species showed higher levels of gelatin activity, which may correlate to the seMMP-9 enzymes. The variability observed in the composition of these venoms may be related to the tribe phylogeny and influenced by their diets. In the presented study, we expanded the set of venomics studies of the Philodryadini tribe, which paves new roads for further studies on the evolution and ecology of Dipsadidae snakes.

Comparing morphological and secretory aspects of cephalic glands among the New World coral snakes brings novel insights on their biological roles

Oral and other cephalic glands have been surveyed by several studies with distinct purposes. Despite the wide diversity and medical relevance of the New World coral snakes, studies focusing on understanding the biological roles of the glands within this group are still scarce. Specifically, the venom glands of some coral snakes were previously investigated but all other cephalic glands remain uncharacterized. In this sense, performing morphological and molecular analysis of these glands may help better understand their biological role. Here, we studied the morphology of the venom, infralabial, rictal, and harderian glands of thirteen species of Micrurus and Micruroides euryxanthus. We also performed a molecular characterization of these glands from selected species of Micrurus using transcriptomic and proteomic approaches. We described substantial morphological variation in the cephalic glands of New World coral snakes and structural evidence for protein-secreting cells in the inferior rictal glands. Our molecular analysis revealed that the venom glands, as expected, are majorly devoted to toxin production, however, the infralabial and inferior rictal glands also expressed some toxin genes at low to medium levels, despite the marked morphological differences. On the other hand, the harderian glands were dominated by the expression of lipocalins, but do not produce toxins. Our integrative analysis, including the prediction of biological processes and pathways, helped decipher some important traits of cephalic glands and better understand their biology.

Patterns of morphological variation and ecological correlates in the skull of vipers (Serpentes: Viperidae)

The skull of vipers is a highly kinetic anatomical structure involved in envenomating and consuming of prey. Morphological knowledge about the viperid skull is based on studies on some groups of species, but information on its variation within the whole family and its functional morphology is still scarce. In this study, we aimed to explore variation in skull morphology among species of the three subfamilies of Viperidae, and test whether that variation correlates with macrohabitat and diet. We performed quantitative analyses of the viperid skull based on broad taxonomic sampling and two methodological approaches: linear and geometric morphometrics. The results of both approaches showed that much of the variation lies in differences of shape and relative size of the premaxilla, the nasals, the frontals, and the parietals. The results indicated that phylogeny and size influence the shape of the skull, but we also found evidence of morphological differentiation between arboreal and terrestrial species and in species with mammal specialist diet. Our findings imply that, besides evolutionary allometry and phylogenetic signal, demands of particular diets coupled with use of certain habitats have in part shaped morphological evolution of the viperid skull.

The venom composition of the snake tribe Philodryadini: ‘Omic’ techniques reveal intergeneric variability among South American racers

Snakes of the Philodryadini tribe are included in the Dipsadidae family, which is a diverse group of rear-fanged snakes widespread in different ecological conditions, including habitats and diet. However, little is known about the composition and effects of their venoms despite their relevance for understanding the evolution of these snakes or even their impact on the occasional cases of human envenoming. In this study, we integrated venom gland transcriptomics, venom proteomics and functional assays to characterize the venoms from eight species of the Philodryadini tribe, which includes the genus Philodryas, Chlorosoma and Xenoxybelis. The most abundant components identified in the venoms were snake venom metalloproteinases (SVMPs), cysteine-rich secretory proteins (CRISPs), C-type lectins (CTLs), snake endogenous matrix metalloproteinases type 9 (seMMP-9) and snake venom serinoproteinases (SVSPs). These protein families showed a variable expression profile in each genus. SVMPs were the most abundant components in Philodryas, while seMMP-9 and CRISPs were the most expressed in Chlorosoma and Xenoxybelis, respectively. Lineage-specific differences in venom composition were also observed among Philodryas species, whereas P. olfersii presented the highest amount of SVSPs and P. agassizii was the only species to express significant amounts of 3FTx. The variability observed in venom composition was confirmed by the venom functional assays. Philodryas species presented the highest SVMP activity, whereas Chlorosoma species showed higher levels of gelatin activity, which may correlate to the seMMP-9 enzymes. The variability observed in the composition of these venoms may be related to the tribe phylogeny and influenced by their diets. In the presented study, we expanded the set of venomics studies of the Philodryadini tribe, which paves new roads for further studies on the evolution and ecology of Dipsadidae snakes.

Independent Recruitment of Different Types of Phospholipases A2 to the Venoms of Caenophidian Snakes: The Rise of PLA2-IIE within Pseudoboini (Dipsadidae)

Snake venoms harbor a wide and diverse array of enzymatic and nonenzymatic toxic components, allowing them to exert myriad effects on their prey. However, they appear to trend toward a few optimal compositional scaffolds, dominated by four major toxin classes: SVMPs, SVSPs, 3FTxs, and PLA2s. Nevertheless, the latter appears to be restricted to vipers and elapids, as it has never been reported as a major venom component in rear-fanged species. Here, by investigating the original transcriptomes from 19 species distributed in eight genera from the Pseudoboini tribe (Dipsadidae: Xenodontinae) and screening among seven additional tribes of Dipsadidae and three additional families of advanced snakes, we discovered that a novel type of venom PLA2, resembling a PLA2-IIE, has been recruited to the venom of some species of the Pseudoboini tribe, where it is a major component. Proteomic and functional analyses of these venoms further indicate that these PLA2s play a relevant role in the venoms from this tribe. Moreover, we reconstructed the phylogeny of PLA2s across different snake groups and show that different types of these toxins have been recruited in at least five independent events in caenophidian snakes. Additionally, we present the first compositional profiling of Pseudoboini venoms. Our results demonstrate how relevant phenotypic traits are convergently recruited by different means and from homologous and nonhomologous genes in phylogenetically and ecologically divergent snake groups, possibly optimizing venom composition to overcome diverse adaptative landscapes.

Independent recruitment of different types of Phospholipases A2 to the venoms of Caenophidian snakes: the rise of PLA2-IIE within Pseudoboini (Dipsadidae)

Snake venoms harbor a wide and diverse array of enzymatic and nonenzymatic toxic components, allowing them to exert myriad effects on their prey. However, they appear to trend toward a few optimal compositional scaffolds, dominated by four major toxin classes: SVMPs, SVSPs, 3FTxs, and PLA2s. Nevertheless, the latter appears to be restricted to vipers and elapids, as it has never been reported as a major venom component in rear-fanged species. Here, by investigating the original transcriptomes from 19 species distributed in eight genera from the Pseudoboini tribe (Dipsadidae: Xenodontinae) and screening among seven additional tribes of Dipsadidae and three additional families of advanced snakes, we discovered that a novel type of venom PLA2, resembling a PLA2-IIE, has been recruited to the venom of some species of the Pseudoboini tribe, where it is a major component. Proteomic and functional analyses of these venoms further indicate that these PLA2s play a relevant role in the venoms from this tribe. Moreover, we reconstructed the phylogeny of PLA2s across different snake groups and show that different types of these toxins have been recruited in at least five independent events in caenophidian snakes. Additionally, we present the first compositional profiling of Pseudoboini venoms. Our results demonstrate how relevant phenotypic traits are convergently recruited by different means and from homologous and nonhomologous genes in phylogenetically and ecologically divergent snake groups, possibly optimizing venom composition to overcome diverse adaptative landscapes.

Venom phenotype conservation suggests integrated specialization in a lizard-eating snake

Biological specialization reduces the size of niche space while increasing efficiency in the use of available resources. Specialization often leads to phenotypic changes via natural selection aligning with niche space constraints. Commonly observed changes are in size, shape, behavior, and traits associated with feeding. One often selected trait for dietary specialization is venom, which, in snakes, often shows variation dependent on diet across and within species. The Neotropical Blunt-headed Treesnake (Imantodes cenchoa) is a highly specialized, rear-fanged, arboreal, lizard hunter that displays a long thin body, enlarged eyes, and a large Duvernoy's gland. However, toxin characterization of I. cenchoa has never been completed. Here, we use RNA-seq and mass spectrometry to assemble, annotate, and analyze the venom gland transcriptomes of four I. cenchoa from across their range. We find a lack of significant venom variation at the sequence and expression levels, suggesting venom conservation across the species. We propose this conservation provides evidence of a specialized venom repertoire, adapted to maximize efficiency of capturing and processing lizards. Importantly, this study provides the most complete venom gland transcriptomes of I. cenchoa and evidence of venom specialization in a rear-fanged snake, giving insight into selective pressures of venom across all snake species.

Total-evidence phylogeny and evolutionary morphology of New World pitvipers (Serpentes: Viperidae: Crotalinae)

Crotalines (pitvipers) in the Americas are distributed from southern Canada to southern Argentina, and are represented by 13 genera and 163 species that constitute a monophyletic group. Their phylogenetic relationships have been assessed mostly based on DNA sequences, while morphological data have scarcely been used for phylogenetic inquiry. We present a total-evidence phylogeny of New World pitvipers, the most taxon/character comprehensive phylogeny to date. Our analysis includes all genera, morphological data from external morphology, cranial osteology and hemipenial morphology, and DNA sequences from mitochondrial and nuclear genes. We performed analyses with parsimony as an optimality criterion, using different schemes for character weighting. We evaluated the contribution of the different sources of characters to the phylogeny through analyses of reduced datasets and calculation of weighted homoplasy and retention indexes. We performed a morphological character analysis to identify synapomorphies for the main clades. In terms of biogeography, our results support a single colonization event of the Americas by pitvipers, and a cladogenetic event into a Neotropical clade and a North American/Neotropical clade. The results also shed light on the previously unstable position of some taxa, although they could not sufficiently resolve the position of Bothrops lojanus, which may lead to the paraphyly of either Bothrops or Bothrocophias. The morphological character analyses demonstrated that an important phylogenetic signal is contained in characters related to head scalation, the jaws and the dorsum of the skull, and allowed us to detect morphological convergences in external morphology associated with arboreality.

Phylogenetic and morphological evidence reveals the association between diet and the evolution of the venom delivery system in Neotropical goo-eating snakes

Advanced endoglyptodont snakes share a complex but homologous venom delivery system associated with the upperjaw and its dentition. Recently, a remarkable novel lower jaw venom delivery system was described for the Neotropicaldipsadine radiation of goo-eating snakes. While most dipsadines are opistoglyphous and exhibit large, mainly serousvenom glands associated with the upper jaw and supralabial glands, goo-eating dipsadine snakes are aglyphous and lackserous upper labial venom glands. Here, we provide new morphological and histological information on the oral glandsand maxillary dentition of representatives of the major lineages of dipsadines that help trace the evolutionary steps thatshaped the venom delivery system of dipsadines. We performed a maximum likelihood analysis on a molecular datasetthat includes 443 terminals and seven loci. Our results show that goo-eating dipsadines form a monophyletic assemblagethat includes the genusAdelphicosfor the first time, along withGeophis,Atractus,Ninia,Chersodromus,Tropidodipsas,Sibon, andDipsas. We also provide the first evidence of a complete shift from an upper jaw to a lower jaw venomdelivery system associated with their specialized feeding behaviour. Unlike other dipsadines who exhibit typicalendoglyptodont anteroposteriorly ridged posterior maxillary teeth, goo-eating dipsadines have uniform lateromediallyridged teeth throughout their maxilla. Our results indicate that the loss of the endoglyptodont venom delivery systemoccurred in the most recent common ancestor of goo-eating dipsadines, probably resulting from the loss of theembryonic posterior maxillary lamina responsible for the development of the venom delivery system.

Increasing taxon sampling suggests a complete taxonomic rearrangement in Echinantherini (Serpentes: Dipsadidae)

Although the recent advances on the relationship of its major groups, the systematics of the rich fauna of Neotropical snakes is far from being a consensus. In this sense, derived groups presenting continental distributions have represented a main challenge. The taxonomy of the snake tribe Echinantherini is one of the most contentious among the diverse family known as Dipsadidae. The tribe is poorly sampled in phylogenetic studies, resulting in conflicting hypotheses of relationships among its taxa. Moreover, several rare and micro endemic species of Echinantherini have never been evaluated within a comprehensive phylogenetic framework. Here, we assess for the first time the phylogenetic position of the rare Echinanthera amoena within Echinantherini. We based our analyses on a comprehensive multilocus dataset including 14 of the 16 species described for the tribe. Our results support the monophyly of Echinantherini and strongly indicate E. amoena as a unique lineage, phylogenetically positioned apart from all other congeners. From the three current genera (Echinanthera, Taeniophallus, and Sordellina) our results indicate that Echinanthera and Taeniophallus are paraphyletic, since the T. affinis species group is positioned as sister to Echinanthera (except E. amoena) clustering apart from the clade formed by the T. brevirostris and T. occipitalis groups. We describe new genera for the T. affinis and T. occipitalis species groups and an additional monospecific genus for E. amoena. Although we did not evaluate the phylogenetic position of T. nebularis, we described a new genus and removed it from Echinantherini since its morphology strikingly departs from all species now included in the tribe. Finally, we redefine the genera Echinanthera and Taeniophallus and we provide comments about further directions to study the biogeography and the evolution of morphological traits in Echinantherini.

Revealing the cryptic diversity of the widespread and poorly known South American blind snake genus Amerotyphlops (Typhlopidae: Scolecophidia) through integrative taxonomy

Morphological stasis is generally associated with relative constancy in ecological pressures throughout time, producing strong stabilizing selection that retains similar shared morphology. Although climate and vegetation are commonly the main key factors driving diversity and phenotypic diversification in terrestrial vertebrates, fossorial organisms have their morphology mostly defined by their fossorial lifestyle. Among these secretive fossorial organisms, blind snakes of the South American genus Amerotyphlops are considered poorly studied when compared to other taxa. Here, we evaluate the cryptic diversity of Amerotyphlops using phylogenetic and multivariate approaches. We based our phylogenetic analysis on a molecular dataset composed of 12 gene fragments (eight nuclear and four mitochondrial) for 109 species of Typhlopidae. The multivariate analysis was implemented using 36 morphological variables for 377 specimens of Amerotyphlops. Additionally, we contrast our phylogenetic result with the morphological variation found in cranial, external and hemipenial traits. Our phylogenetic results recovered with strong support the following monophyletic groups within Amerotyphlops: (1) a clade formed by A. tasymicris and A. minuisquamus; (2) a clade composed of A. reticulatus; (3) a north-eastern Brazilian clade including A. yonenagae, A. arenensis, A. paucisquamus and A. amoipira; and (4) a clade composed of A. brongersmianus and a complex of cryptic species. Based on these results we describe four new species of Amerotyphlops from north-eastern and south-eastern Brazil, which can be distinguished from the morphologically similar species, A. brongersmianus and A. arenensis.

Increasing taxon sampling suggests a complete taxonomic rearrangement in Echinantherini (Serpentes: Dipsadidae)

Although the recent advances on the relationship of its major groups, the systematics of the rich fauna of Neotropical snakes is far from being a consensus. In this sense, derived groups presenting continental distributions have represented a main challenge. The taxonomy of the snake tribe Echinantherini is one of the most contentious among the diverse family known as Dipsadidae. The tribe is poorly sampled in phylogenetic studies, resulting in conflicting hypotheses of relationships among its taxa. Moreover, several rare and micro endemic species of Echinantherini have never been evaluated within a comprehensive phylogenetic framework. Here, we assess for the first time the phylogenetic position of the rare Echinanthera amoena within Echinantherini. We based our analyses on a comprehensive multilocus dataset including 14 of the 16 species described for the tribe. Our results support the monophyly of Echinantherini and strongly indicate E. amoena as a unique lineage, phylogenetically positioned apart from all other congeners. From the three current genera (Echinanthera, Taeniophallus, and Sordellina) our results indicate that Echinanthera and Taeniophallus are paraphyletic, since the T. affinis species group is positioned as sister to Echinanthera (except E. amoena) clustering apart from the clade formed by the T. brevirostris and T. occipitalis groups. We describe new genera for the T. affinis and T. occipitalis species groups and an additional monospecific genus for E. amoena. Although we did not evaluate the phylogenetic position of T. nebularis, we described a new genus and removed it from Echinantherini since its morphology strikingly departs from all species now included in the tribe. Finally, we redefine the genera Echinanthera and Taeniophallus and we provide comments about further directions to study the biogeography and the evolution of morphological traits in Echinantherini.

Evolutionary allometry and ecological correlates of fang length evolution in vipers

Traits for prey acquisition form the phenotypic interface of predator–prey interactions. In venomous predators, morphological variation in venom delivery apparatus like fangs and stingers may be optimized for dispatching prey. Here, we determine how a single dimension of venom injection systems evolves in response to variation in the size, climatic conditions and dietary ecology of viperid snakes. We measured fang length in more than 1900 museum specimens representing 199 viper species (55% of recognized species). We find both phylogenetic signal and within-clade variation in relative fang length across vipers suggesting both general taxonomic trends and potential adaptive divergence in fang length. We recover positive evolutionary allometry and little static allometry in fang length. Proportionally longer fangs have evolved in larger species, which may facilitate venom injection in more voluminous prey. Finally, we leverage climatic and diet data to assess the global correlates of fang length. We find that models of fang length evolution are improved through the inclusion of both temperature and diet, particularly the extent to which diets are mammal-heavy diets. These findings demonstrate how adaptive variation can emerge among components of complex prey capture systems.

Características para aquisição de presas formam a interface fenotípica das interações predador-presa. Em predadores venenosos, a variação morfológica no aparelho de entrega de veneno, como presas e ferrões, pode ser otimizada para despachar presas. Aqui, determinamos como uma única dimensão dos sistemas de injeção de veneno evolui em resposta à variação no tamanho, condições climáticas e ecologia alimentar de cobras viperídeos. Medimos o comprimento das presas em mais de 1.900 espécimes de museus representando 199 espécies de víboras (55% das espécies reconhecidas). Encontramos tanto o sinal filogenético quanto a variação dentro do clado no comprimento relativo das presas entre as víboras, sugerindo tendências taxonômicas gerais e potencial divergência adaptativa no comprimento das presas. Recuperamos alometria evolutiva positiva e pouca alometria estática no comprimento das presas. Presas proporcionalmente mais longas evoluíram em espécies maiores, o que pode facilitar a injeção de veneno em presas mais volumosas. Por fim, aproveitamos os dados climáticos e de dieta para avaliar os correlatos globais do comprimento das presas. Descobrimos que os modelos de evolução do comprimento das presas são melhorados através da inclusão de temperatura e dieta, particularmente na medida em que as dietas são dietas pesadas para mamíferos. Essas descobertas demonstram como a variação adaptativa pode surgir entre os componentes de sistemas complexos de captura de presas.

The systematics of Tachymenini (Serpentes, Dipsadidae): an updated classification based on molecular and morphological evidence

Despite the recent advances in the systematics of snakes, the diversity of several Neotropical groups of species remains poorly understood. The lack of studies focused on the phylogenetic relationship within most of the 20 tribes of Dipsadidae precludes a better understanding of the evolution of this diverse family. Here, we present a comprehensive phylogenetic analysis of Tachymenini, a heterogeneous tribe that comprises 36 viviparous species of dipsadids, grouped in seven genera based on morphological similarities. The tribe is widely distributed throughout South America presenting very distinctive phenotypes, habitats, and behaviours. The phylogenetic relationship among tachymenins is a well-recognized challenge regarding the systematics of the South American dipsadids. The similar morphotype of some generalist species, combined with the very derived morphology of some strict specialists, creates a complexity of traits that has prevented the comprehension of the systematics of the group. To address such a challenge, we combine molecular (six loci) and morphological (70 characters) datasets in an integrative phylogenetic approach. The resultant phylogenetic trees indicate, with strong support, that three of the seven current recognized genera (Tachymenis, Tomodon, and Thamnodynastes) are non-monophyletic and, consequently, we propose a new systematic arrangement for Tachymenini. We revalidate two genera, Dryophylax and Mesotes, and we describe three additional monotypic genera, Apographon gen. n., Tachymenoides gen. n., and Zonateres gen. n. to accommodate Tomodon orestes, Tachymenis affinis, and Thamnodynastes lanei, respectively. We also include Tomodon ocellatus and Pseudotomodon trigonatus in Tachymenis and describe a new genus, Galvarinus gen. n., to accommodate the Tachymenis chilensis species group. Furthermore, we also provide an evolutionary scenario for the speciation events based on a time-calibrated tree, commenting on the diversification and origin of the tribe, and on the probable existence of undescribed species of Mesotes and Dryophylax.

The skull of Sanajeh indicus, a Cretaceous snake with an upper temporal bar, and the origin of ophidian wide-gaped feeding

Recent phylogenetic analyses differ in their interpretations of the origin and interrelationships of snakes, resulting in polarized views of snake ecology, habit and acquisition of features associated with wide-gaped feeding (macrostomy). Here, we report a new specimen of the Late Cretaceous nest predator Sanajeh indicus that helps to resolve the origin of macrostomy. The new specimen preserves an ossified upper temporal bar and a posteriorly expanded otooccipital region that lacks a free-ending supratemporal bone and retains a lizard-like palatomaxillary arch that allows limited movements during swallowing. Phylogenetic analyses of a large-scale total evidence dataset resolve Sanajeh near the base of Pan-Serpentes, as the sister group of Najash, Dinilysia and crown-group Serpentes. The Cretaceous Tetrapodophis and Coniophis represent the earliest-diverging members of Pan-Serpentes. The Cretaceous hindlimbed pachyophiids and Cenozoic Australian ‘madtsoiids’ are inside crown Alethinophidia, whereas mosasaurs are recovered invariably within anguimorphs. Our results suggest that the wide-gape condition in mosasaurs and snakes might have evolved independently, as functionally distinct mechanisms of prey ingestion. The intermediate morphology preserved in Sanajeh indicates that ingestion of large prey items (macrophagy) preceded wide-gaped, unilateral feeding (macrostomy), which appeared 35 Myr later, in the common ancestor of pachyophiids, Cenozoic Australian ‘madtsoiids’ and alethinophidians.